Effective high-temperature wetting has presented a significant challenge in the die casting field for some time. Conventional methods, such as disclosed in U.S. Pat. No. 6,192,968 issued to Renkl, comprise spraying the mold or die walls with a mixture of die-wall treatment agent and water each time a part is removed from the die. This application simultaneously cools the surface of the die walls and applies the treatment agent thereto. However, a drawback of this method is the so-called “Leidenfrost effect”: When the droplets of spray land on the hot surface of the die wall, a vapor barrier forms between the droplets and the surface. This barrier prevents the droplets from completely wetting the surface. Some of the sprayed-on mixture of treatment agent and water therefore runs off the surface of the die wall without cooling, lubricating, or wetting it, thereby failing to impart the desired release properties. Because of this disadvantageous side-effect it is necessary in conventional practice, in order to both cool the die wall surface and coat it with an effective amount of a treatment agent, to apply an excess of the treatment agent/water mixture. This excess will run off the surface of the mold walls unused and then must be collected and disposed of. This may, in some instances, raise significant environmental concerns.
In addition to disposal concerns and the expense of applying excess treatment agent, it is undesirable to continually submit die surfaces to the extreme temperature variations occasioned by the application of the treatment agent/water mixture. The die itself is already subject to a very large temperature gradient in that the inner regions of the die may be at about 450° F., while the outer surface during operation may reach in excess of 1300° F. This temperature difference causes heat checking. Further, when a treatment-agent/water mixture is used to cool the die surface, the surface temperature may be lowered to between about 300° F. and 350° F. This may, in certain cases, exacerbate the heat checking to the point that the die produces parts outside of acceptable tolerances, thus effectively rendering the die useless (at least for the particular item being formed).
It is further undesirable to use excess lubricant for the reason that, during casting, the lubricants may be incorporated into cast parts, thereby potentially causing deformations, weak spots, and/or unpaintable/unfinishable spots.
Known wetting compositions include emulsions of methyl alkyl/methyl propyl-benzyl polysiloxane fluids, known as paintable silicone fluid emulsions. These fluids are those that are made from methyl-hydrogen silicone fluid. While paintable silicone fluid emulsions are effective at wetting surfaces up to about 800° F., they are expensive and tend to build up on the die surface.
In addition to the foregoing, it is also the case that applying an even film to high temperature surfaces on dies for casting of molten metals (e.g., die casting) and hot forming of metals has long been a problem. Most water-based substances that are used as parting agents for these operations, called mold, die or forging lubricants, do not wet the hottest areas of the die as well as the cooler areas. In areas of the die where the temperature exceeds 600° F., the wetting of most die lubricants is reduced. In areas of the die where the temperature exceeds 700° F., the wetting of most die lubricants is so poor that excessive quantities thereof must be sprayed onto the die so that the water carrier first reduces the temperature of the hot area, after which the lubricant forms a film. Excessive spraying of hot areas results is excessive deposition onto the cooler adjacent areas. Further, excessive lubrication application can cause buildup on the die surface.
Thus, it would be desirable to provide a wetting composition that effectively wets and/or lubricates a high temperature metal surface without having to apply an excess of the composition to the die surface, thus substantially eliminating waste and/or disposal concerns. It would further be desirable to provide such a composition which does not contain compounds deleteriously affecting either mechanical properties of a cast part, or finishing/painting operations upon the cast part. Still further, it would be desirable to provide such a composition which has, as its main ingredient, environmentally friendly compound(s) which are both abundant and relatively inexpensive.